JP2021086115A - Image forming apparatus and color shift correction method - Google Patents

Abstract

To correct color shift while ensuring productivity.SOLUTION: An image forming apparatus according to an aspect of the present invention comprises a color shift correction unit that performs correction of color shift in an image formed of a plurality of colors, and when image formation is performed without using a predetermined reference color, the color shift correction unit performs the correction on the basis of positional deviation between pattern images that are formed for each of the plurality of colors used in the image formation.SELECTED DRAWING: Figure 13

Description

The present invention relates to an image forming apparatus and a color shift correction method.

Conventionally, in an image forming apparatus that forms a color image using a plurality of colors, a positional deviation of each color toner image formed on an intermediate transfer belt that transfers the toner image to a recording medium with respect to a reference color toner image is detected, and the detection result is obtained. A technique for correcting color shift is known based on the above.

Further, a technique for calculating an average value of the amount of misalignment of each color with respect to a reference color and correcting the color misalignment based on this value is disclosed (see, for example, Patent Document 1).

However, in the conventional technique, in the print mode in which an image is formed without using a reference color, the positional deviation of each color toner image with respect to the reference color toner image cannot be detected and the color deviation cannot be corrected. Therefore, all colors including the reference color cannot be corrected. After switching to the print mode for forming an image using, the color shift is corrected. This may reduce productivity.

An object of the present invention is to secure productivity and correct color shift.

The image forming apparatus according to one aspect of the present invention includes a color shift correction unit that corrects color shift of an image formed of a plurality of colors, and the color shift correction unit does not use a predetermined reference color for an image. When forming, the correction is performed based on the positional deviation between the pattern images formed for each of a plurality of colors used in image formation.

According to the present invention, productivity can be ensured and color shift can be corrected.

It is a figure which shows the whole structure example of the image forming apparatus which concerns on embodiment. It is a figure which shows the structural example of the image-forming part which concerns on embodiment. It is the figure of the image-making part which changed the arrangement in the traveling direction of an intermediate transfer belt. It is a figure which shows the case where the image-forming part which is not used for image formation is separated. It is a figure of the structural example of the scanning optical system which concerns on embodiment. It is a block diagram of the hardware configuration example of the light beam scanning part which concerns on embodiment. It is a block diagram of the configuration example of the VCO clock generation part which concerns on embodiment. It is a block diagram of the configuration example of the writing start position control part which concerns on embodiment. It is a timing chart of the main scanning direction writing start control which concerns on embodiment. It is a timing chart of the sub-scanning direction writing start control which concerns on embodiment. It is a figure which shows the configuration example of the line memory which concerns on embodiment. It is a flowchart of the image formation operation example which concerns on embodiment. It is a figure which shows the functional structure example of the printer control part which concerns on 1st Embodiment. It is a figure of the correction toner image example corresponding to the structure of FIG. It is a figure of the correction toner image example corresponding to the structure of FIG. It is a figure of the correction toner image example corresponding to the structure of FIG. It is a figure which shows an example of a reference position. It is a flowchart which shows the color shift correction operation example which concerns on 1st Embodiment. It is a figure which shows the functional structure example of the printer control part which concerns on 2nd Embodiment. It is a flowchart which shows the color shift correction operation example which concerns on 2nd Embodiment.

Hereinafter, modes for carrying out the invention will be described with reference to the drawings. In each drawing, the same components may be designated by the same reference numerals and duplicate description may be omitted.

In the embodiment, a color shift correction unit for correcting color shift of an image formed by a plurality of colors is provided, and this color shift correction unit is used for image formation when an image is formed without using a predetermined reference color. The color shift is corrected based on the positional shift between the pattern images formed for each of the plurality of colors used.

As a result, even in the print mode in which the image is formed without using the reference color, it is not necessary to switch to the print mode in which the image is formed in all colors including the reference color, and the productivity is ensured and the color shift is corrected.

<Terms in the embodiment>
(Print mode)
Information indicating whether or not to form an image using a predetermined reference color. In the embodiment, the print mode in which the image is formed using the reference color is set as the first print mode, and the print mode in which the image is formed without using the reference color is set as the second print mode.

(Color shift)
The color shift is a general term for the position shift of the image of each color in the main scanning direction, the magnification error in the main scanning direction, and the position shift in the sub-scanning direction in the image formed by a plurality of colors. Further, the correction of color shift means to correct the image forming apparatus so that the color shift is eliminated.

(Main scanning direction)
The direction in which the light beam is scanned by the light beam scanning unit on the photoconductor drum. It corresponds to the direction along the rotation axis of the photoconductor drum.

(Secondary scanning direction)
The direction orthogonal to the main scanning direction. The traveling direction of the intermediate transfer belt corresponds to the sub-scanning direction.

(Magnification error in the main scanning direction)
The magnification in the main scanning direction means the imaging magnification in the main scanning direction of the image formed on the photoconductor drum by the scanning lens. Further, the magnification error in the main scanning direction means an error in the magnification in the main scanning direction caused by fluctuations in characteristics such as the refractive index and surface shape of the scanning lens.

(Correction toner image)
It is a toner image used for correcting color shift, and is an example of a pattern image. The correction toner image in the embodiment is a toner image formed on the intermediate transfer belt.

It should be noted that image formation and printing in the terms of the embodiment are synonymous.

Hereinafter, embodiments will be described using an electrophotographic image forming apparatus including a secondary transfer mechanism called a tandem system as an example. The image forming apparatus is an MFP (Multifunction Peripheral Printer Product) in which a copy function, a print function, a facsimile function, and the like are mounted in one housing.

<Overall configuration example of image forming apparatus 100>
FIG. 1 is a diagram illustrating an example of the overall configuration of the image forming apparatus 100. The image forming apparatus 100 includes an intermediate transfer unit in the center, and the intermediate transfer unit includes an intermediate transfer belt 10 which is an endless belt. The intermediate transfer belt 10 is hung around the first support roller 14, the second support roller 15, and the third support roller 16 and is rotationally driven clockwise.

Further, the image forming apparatus 100 includes an intermediate transfer body cleaning unit 17 on the right side of the second support roller 15 for removing residual toner remaining on the intermediate transfer belt 10 after transferring the toner image to the recording medium P. ..

A yellow (Y) image-forming part, a magenta (M) image-forming part, and a cyan (C) image-forming part facing the intermediate transfer belt 10 arranged between the first support roller 14 and the second support roller 15. An image forming section 20 composed of an image forming section and a black (K) image forming section is provided, and image forming sections of each color are juxtaposed along the traveling direction of the intermediate transfer belt 10.

The image forming unit of each color has the same configuration except that the color of the toner used is different. Therefore, in the description and drawings, the subscripts "Y", "M", "C", and "K" indicating the color of the toner to be used will be omitted as appropriate. Further, the image forming apparatus 100 also includes a white (W) image forming portion on the upstream side of the yellow (Y) image forming portion in the traveling direction of the intermediate transfer belt 10, but this illustration is omitted in FIG. , FIG.

The image forming unit 20 includes a photoconductor drum 40 of each color, a charging unit 18, a developing unit, and a cleaning unit, and is detachably attached to the image forming apparatus 100.

Further, the image forming apparatus 100 includes an optical beam scanning unit 21 above the image forming unit 20. The light beam scanning unit 21 irradiates the photoconductor drum 40 of each color with a light beam (laser light) for image formation, so that the photoconductor drum 40 of each color is subjected to an electrostatic latent image (latent image) according to the image data. Image image) can be formed.

The electrostatic latent image of the photoconductor drum 40 of each color is developed by the developing unit, and the developed toner image of each color is superposed on the intermediate transfer belt 10 and primarily transferred. As a result, a color toner image is formed on the intermediate transfer belt 10. The toner image is supported on the intermediate transfer belt 10 and is moved (conveyed) along the traveling direction of the intermediate transfer belt 10. The configuration of the image forming unit 20 will be described in detail separately with reference to FIG.

The image forming apparatus 100 includes a secondary transfer unit 22 below the intermediate transfer belt 10. The secondary transfer unit 22 is arranged so that the secondary transfer belt 24, which is an endless belt, is bridged between the two rollers 23, and the intermediate transfer belt 10 is pushed up and pressed against the third support roller 16. The secondary transfer belt 24 can secondary transfer the toner image formed on the intermediate transfer belt 10 onto the recording medium P.

Further, the image forming apparatus 100 includes a fixing unit 25 on the side of the secondary transfer apparatus 22. The fixing unit 25 fixes the toner image on the recording medium P, which has been conveyed with the toner image secondarily transferred, to the recording medium P. The fixing unit 25 includes a fixing roller 26 which is an endless belt and a pressure roller 27, and records a toner image transferred to the surface of the recording medium P by the heat and pressure of the fixing roller 26 and the pressure roller 27. It can be fixed on the medium P.

Further, the image forming apparatus 100 inverts the front and back of the recording medium P in order to form an image on the back surface of the recording medium P immediately after the image is formed on the front surface below the secondary transfer unit 22 and the fixing unit 25. The sheet reversing unit 28 is provided.

Next, a series of steps in which an image is formed on the recording medium P in the image forming apparatus 100 will be described.

When the start button of "copy" in the operation unit (not shown) is pressed, the image forming apparatus 100 places the document on the document feeding table 30 of the ADF (Auto Document Feeder) 400, which is the automatic document transporting unit. If so, the ADF 400 transports the document toward the contact glass 320. On the other hand, when the original is not placed on the original paper feed tray 30, an image reading unit including a first carriage 33 and a second carriage 34 for reading the original manually placed on the contact glass 320. Drive 300.

In the image reading unit 300, the light source included in the first carriage 33 irradiates the contact glass 320 with light. The reflected light from the document surface is reflected toward the second carriage 34 by the first mirror included in the first carriage 33, and is reflected by the mirror included in the second carriage 34. Then, the reflected light from the document surface is imaged on the imaging surface of the CCD (Charge Coupled Device) 36, which is a reading sensor, by the imaging lens 35. The CCD 36 captures an image of the original surface, and image data of each color of Y, M, C, and K is generated based on the image signal captured by the CCD 36.

Further, the image forming apparatus 100 receives a fax (Facsimile) output instruction when the "print" start button is pressed or when an image forming instruction is given from an external device such as a PC (Personal Computer). Occasionally, the rotation drive of the intermediate transfer belt 10 is started, and image drawing preparation is performed for each unit of the image forming unit 20.

After that, the image forming apparatus 100 starts the image forming process of each color. The photoconductor drum 40 for each color is irradiated with a laser modulated based on the image data of each color, and an electrostatic latent image is formed. Then, the toner images of each color in which the electrostatic latent image is developed are superposed on the intermediate transfer belt 10 as a single image to be formed.

After that, at the timing when the tip of the toner image on the intermediate transfer belt 10 enters the secondary transfer unit 22, the recording medium P 2 is timed so that the tip of the recording medium P enters the secondary transfer unit 22. It is sent to the next transfer unit 22. Then, the toner image on the intermediate transfer belt 10 is secondarily transferred to the recording medium P by the secondary transfer unit 22. The paper on which the toner image is secondarily transferred is sent to the fixing unit 25, and the toner image is fixed on the recording medium P.

Here, the paper feeding of the recording medium P up to the secondary transfer position will be described. The recording medium P is fed out from one of the paper feed trays 44 provided in the paper feed unit 43 in multiple stages by rotationally driving one of the paper feed rollers 42 of the paper feed table 200. After that, only one sheet is separated by the separation roller 45, enters the transfer roller unit 46, and is conveyed by the transfer roller 47. After that, it is guided to the transfer roller unit 48 in the image forming apparatus 100, is abutted against the resist roller 49 of the transfer roller unit 48, and is temporarily stopped, and then, as described above, is secondary in accordance with the timing of the secondary transfer. It is sent out toward the transfer unit 22.

Further, the user can insert the recording medium P into the manual feed tray 51 and feed the paper. When the user inserts the recording medium P into the manual feed tray 51, the image forming apparatus 100 rotates and drives the paper feed roller 50 to separate one of the recording media P on the manual feed tray 51 and manually feeds the paper feed path. Pull in to 53. Then, in the same manner as described above, the resist roller 49 is abutted against the resist roller 49 to be temporarily stopped, and then sent out to the secondary transfer unit 22 at the timing of the secondary transfer described above.

The recording medium P fixed and discharged by the fixing unit 25 is guided by the discharge roller 56 by the switching claw 55, discharged by the discharge roller 56, and stacked on the paper discharge tray 57. Alternatively, it is guided to the sheet reversing unit 28 by the switching claw 55, inverted by the sheet reversing unit 28, and guided to the secondary transfer position again. After that, an image is formed on the back surface of the recording medium P, and then the image is ejected onto the paper ejection tray 57 by the ejection roller 56.

On the other hand, the residual toner remaining on the intermediate transfer belt 10 after the image transfer is removed by the intermediate transfer body cleaning unit 17 to prepare for the image formation again.

The image forming apparatus 100 can form a color image on the recording medium P in this way.

<Structure example of image forming unit 20>
Next, the configuration of the image forming unit 20 in the image forming apparatus 100 will be described with reference to FIG. FIG. 2 is a diagram illustrating an example of the configuration of the image forming unit 20 of the image forming apparatus 100. The image forming apparatus 100 combines five sets of image forming units 20 and five sets of light beam scanning units 21 in order to form a color image in which images of five colors (white, yellow, magenta, cyan, and black) are superimposed. Be prepared. The five sets of image forming units 20 and the five sets of optical beam scanning units 21 form white (W), yellow (Y), magenta (M), and cyan along the upstream to downstream of the traveling direction 5 of the intermediate transfer belt 10. (C) and black (K) are juxtaposed in this order.

The light beam scanning unit 21 is drive-modulated according to the image data and selectively emits a light beam. The emitted light beam is deflected by a polygon mirror that rotates with a polygon motor as a drive source, and scans on the photoconductor drum 40. The light beam scanning unit 21 will be described in detail with reference to FIGS. 5 and 6 separately.

The image forming unit 20 of each color includes a charging unit 18, a developing unit 29, a transfer unit 62, a cleaning unit 63, and a static eliminator 19 around the photoconductor drum 40.

The image forming apparatus 100 forms a toner image of the first color (W color) on the intermediate transfer belt 10 by charging, exposing, developing, and transferring, which is an electrophotographic image forming process, and then a second color (Y color). By forming a toner image in the order of the third color (M color), the fourth color (C color), and the fifth color (K color), a toner image of a color in which five color images are superimposed is formed.

Further, the secondary transfer unit 22 transfers the toner image formed on the intermediate transfer belt 10 to the conveyed recording medium P. As a result, a color toner image in which five color toner images are superimposed can be formed on the recording medium P. After that, the toner image on the recording medium P is fixed to the recording medium P by the fixing unit 25 (not shown).

Further, the image forming apparatus 100 detects the correction toner image formed on the intermediate transfer belt 10 at a position facing the first support roller 14 via the intermediate transfer belt 10, and the first sensor 31 and the second sensor. 32 is provided.

The first sensor 31 and the second sensor 32 are reflection type optical sensors, respectively, and are installed at two locations in a direction orthogonal to the traveling direction 5 of the intermediate transfer belt 10 (direction perpendicular to the paper surface). The first sensor 31 and the second sensor 32 output a voltage signal corresponding to the light intensity of the reflected light of the irradiated light.

The light intensity of the reflected light in the region where the correction toner image is not formed on the surface of the intermediate transfer belt 10 and the light intensity of the reflected light in the region where the correction toner image is formed are different. Therefore, the image forming apparatus 100 can detect the correction toner image based on the voltage signal corresponding to the light intensity of the reflected light output by the first sensor 31 and the second sensor 32.

The image forming apparatus 100 receives voltage signals from the first sensor 31 and the second sensor 32, and shifts the positions of the correction toner images of each color formed on the intermediate transfer belt 10 in the main scanning direction and the sub scanning direction. Detects magnification error in the scanning direction. Then, based on the detection result, the toner image on the intermediate transfer belt 10 is secondarily transferred to form an image on the recording medium P, and the main scanning direction, the sub-scanning direction, and the main scanning direction are displaced between the images of each color. Magnification error can be corrected.

Further, the image forming apparatus 100 has a configuration in which the arrangement of the image forming unit 20 of each color can be changed, and the order of the colors to be imaged can be changed in the traveling direction 5 of the intermediate transfer belt 10. FIG. 3 shows an example of the configuration of the image forming unit 20 when the black (K) and the white (W) are exchanged. In this case, since the white toner image is formed on the uppermost layer of the toner image formed on the intermediate transfer belt 10, when the toner image is secondarily transferred to the recording medium P, the white toner image becomes the lowermost layer. It becomes the background image.

Further, as shown in FIG. 4, when a color image of four colors (Y, M, C, K) is formed in a state where the arrangements of black (K) and white (W) are exchanged, white (W) is used. At the image-forming position, the transfer unit 62 and the intermediate transfer belt 10 are separated from the image-creating unit 20. Due to this separation, image formation is performed without using white (W).

Although it is possible to form an image with four colors without separating the image forming units 20 of colors not used in image formation, if the image forming units 20 of colors not used in image forming are operated without separating them. , The toner of this color may be deteriorated or the toner may be wasted. Therefore, for colors that are not used in image formation, it is preferable that the image forming portions 20 are separated from each other and not operated.

<Structure example of scanning optical system 210>
Next, the configuration of the scanning optical system 210 included in the light beam scanning unit 21 of the image forming apparatus 100 will be described with reference to FIG. FIG. 5 is a diagram illustrating an example of the configuration of the scanning optical system 210. The scanning optical system 210 when the light beam scanning unit 21 in FIG. 2 is viewed from above (positive Z direction) is shown. FIG. 5 shows only the scanning optical system 210 for one of the five colors, but since the scanning optical system 210 for the other four colors has the same configuration, a duplicate description will be omitted here.

The light beam emitted from the LD211 reaches the polygon mirror 213 after being beam-shaped by the cylinder lens 212. The reached light beam is deflected according to the rotation of the polygon mirror 213, passes through the fθ lens 214, is folded back by the folded mirror 215, and is irradiated to the photoconductor drum 40. By changing the deflection angle according to the rotation of the polygon mirror 213, the light beam is scanned in the main scanning direction (X direction) on the photoconductor drum 40.

A synchronization mirror 216, a synchronization lens 217, and a synchronization sensor 218 are provided on the writing start side (negative X direction side) in the main scanning direction. Note that "writing" is synonymous with "exposure". Of the light beams that have passed through the fθ lens 214, the light beam on the writing start side is reflected by the synchronous mirror 216 and focused by the synchronous lens 217 toward the light receiving surface of the synchronous sensor 218. The synchronization sensor 218 is composed of a photodiode or the like, and outputs an electric signal according to the intensity of the received light beam.

In this case, since the light beam reaches the light receiving surface of the synchronization sensor 218 at a predetermined cycle according to the rotation of the polygon mirror 213, the electric signal output by the synchronization sensor 218 is used as a synchronization detection signal for synchronizing the start of writing. Available. The optical beam scanning unit 21 can determine the writing start timing in the main scanning direction based on the synchronization detection signal by the synchronization sensor 218.

<Hardware configuration of optical beam scanning unit 21>
Next, FIG. 6 is a block diagram illustrating an example of the hardware configuration of the light beam scanning unit 21. Note that FIG. 6 shows only the light beam scanning unit 21 for one of the five colors, but since the other four colors of the light beam scanning unit 21 have the same configuration, the description is duplicated here. Is omitted.

As shown in FIG. 6, the optical beam scanning unit 21 includes a polygon motor control unit 221, a writing start position control unit 222, an LD control unit 223, a synchronization detection lighting control unit 224, and a pixel clock generation unit 225. And have.

These are composed of electronic circuits such as ASIC (application specific integrated circuit) or FPGA (Field-Programmable Gate Array). However, the present invention is not limited to this, and a CPU (Central Processing Unit) or the like may be used.

Further, the optical beam scanning unit 21 is electrically connected to the printer control unit 1 so as to be able to send and receive data and signals, and operates under the control of the printer control unit 1. The printer control unit 1 is composed of a CPU, a RAM (Random Access Memory), a ROM (Read Only Memory), an ASIC, an external I / F, and the like, and includes a first sensor 31 and a second sensor 32, and a correction data storage unit 229. Is electrically connected to. The printer control unit 1 can control the light beam scanning unit 21 based on the voltage signals and the like input from the first sensor 31 and the second sensor 32.

Next, the operation of each component included in the light beam scanning unit 21 will be described.

At the timing when the light beam scanned by the scanning optical system 210 passes over the synchronization sensor 218, the synchronization sensor 218 is a pixel clock generation unit 225, a synchronization detection lighting control unit 224, and a writing start position control unit 222, respectively. The synchronization detection signal XDETP is output to.

The pixel clock generation unit 225 generates a pixel clock signal PCLK synchronized with the synchronization detection signal XDETP and outputs the pixel clock signal PCLK to the writing start position control unit 222 and the synchronization detection lighting control unit 224.

The synchronization detection lighting control unit 224 turns on the LD forced lighting signal BD to forcibly turn on the LD211 in order to first detect the synchronization detection signal XDETP. After detecting the synchronization detection signal XDETP, the synchronization detection lighting control unit 224 can reliably detect the synchronization detection signal XDETP by using the synchronization detection signal XDETP and the pixel clock signal PCLK to the extent that flare light is not generated. The LD211 is turned on at the timing. After detecting the synchronization detection signal XDETP, an LD forced lighting signal BD that turns off the LD211 is generated and output to the LD control unit 223.

Further, the synchronization detection lighting control unit 224 generates the light amount control timing signal APC of each LD211 for five colors by using the synchronization detection signal XDETP and the pixel clock signal PCLK, and outputs the light amount control timing signal APC to the LD control unit 223. This signal is output during the non-writing period, which is a period other than the period during which the light beam is written (exposed) on the photoconductor drum 40, and the light amount of the light beam emitted by the LD211 during this non-writing period is a predetermined amount of light. Is controlled by.

The LD control unit 223 controls the lighting of the LD 211 according to the image data synchronized with the LD forced lighting signal BD, the light amount control timing signal APC, and the pixel clock signal PCLK. The light beam is emitted from the LD 211, deflected by the polygon mirror 213, and scanned on the photoconductor drum 40 via the fθ lens 214.

The polygon motor control unit 221 controls the rotation of the polygon mirror 213 at a predetermined rotation speed by a control signal from the printer control unit 1.

The writing start position control unit 222 determines the writing start timing and the writing width (toner image width) based on the synchronization detection signal XDETP, the pixel clock signal PCLK, the control signal from the printer control unit 1, and the like. The gate signal XRGATE and the sub-scanning gate signal XFGATE are set.

The pixel clock generation unit 225 includes a phase-locked clock generation unit 226, a VCO (Voltage Controller Oscillator) clock generation unit 227, and a reference clock generation unit 228, and generates a pixel clock that serves as a reference for writing timing.

The VCO clock signal VCLK input from the VCO clock generation unit 227 and the synchronization detection signal XDETP are input to the phase synchronization clock generation unit 226. Further, the phase-locked clock generation unit 226 can output the pixel clock signal PCLK synchronized with the synchronization detection signal XDETP to the synchronization detection lighting control unit 224 or the like.

The reference clock generation unit 228 generates the reference clock signal FREF, and the VCO clock generation unit 227 generates the VCO clock signal VCLK.

The first sensor 31 and the second sensor 32 output a voltage signal for detecting the correction toner image to the printer control unit 1, and the printer control unit 1 shifts the position of the correction toner image of each color based on this voltage signal. The amount and the magnification error in the main scanning direction are acquired, and the correction data for correcting these is acquired. The printer control unit 1 outputs the acquired correction data to the writing start position control unit 222, the pixel clock generation unit 225, and the correction data storage unit 229, and sets or updates the correction data. The writing start position control unit 222 controls the writing start position according to the correction data, and the pixel clock generation unit 225 generates a pixel clock according to the correction data.

The correction data storage unit 229 is composed of an HDD (Hard Disk Drive) or the like included in the image forming apparatus 100, and stores correction data. The stored correction data is read out at the time of image formation, and the color shift is corrected by using this.

<Configuration example of VCO clock generator 227>
Next, the configuration of the VCO clock generation unit 227 will be described with reference to FIG. 7. FIG. 7 is a block diagram illustrating an example of the configuration of the VCO clock generation unit 227.

As shown in FIG. 7, the VCO clock generator 227 includes a phase comparator 231, an LPF (Low Pass Filter) 232, a VCO 233, and a 1 / N frequency divider 234.

The reference clock signal FREF and the clock signal divided into 1 / N by the 1 / N divider 234 are input to the phase comparator 231 from the reference clock generator 228. Further, the phase comparator 231 compares the phases of the falling edges of the two input signals, and outputs an error component with a constant current.

The LPF232 removes the high frequency component from the output of the phase comparator 231 and outputs it to the VCO 233.

The VCO 233 outputs a VCO clock signal VCLK having a predetermined frequency based on the output of the low-pass filter 232.

The 1 / N divider 234 divides the input VCO clock signal VCLK into 1 / N at a set division ratio N.
The VCLK frequency can be changed by changing the FREF frequency and the division ratio N with the control signal from the printer control unit 1. By changing the frequency of VCLK, the frequency of the pixel clock PCLK is also changed.

<Structure example of writing start position control unit 222>
FIG. 8 is a block diagram illustrating an example of the configuration of the writing start position control unit 222 in the image forming apparatus 100. As shown in FIG. 8, the writing start position control unit 222 includes a main scan line synchronization signal generation unit 240, a main scan control signal generation unit 250, and a sub scan control signal generation unit 260.

The main scan line synchronization signal generation unit 240 generates a signal XLSYNC for operating the main scan counter 251 in the main scan control signal generation unit 250 and the sub scan counter 261 in the sub scan control signal generation unit 260.

The main scan control signal generation unit 250 generates the main scan gate signal XRGATE that determines the acquisition timing of the image signal (the write start timing in the main scan direction). Further, the sub-scan control signal generation unit 260 generates a sub-scan gate signal XFGATE that determines the acquisition timing of the image signal (the write start timing in the sub-scan direction).

The main scanning control signal generation unit 250 includes a main scanning counter 251 that operates with XLSYNC and the pixel clock signal PCLK, and a first set value SET1 included in the correction data input from the correction data storage unit 229 via the printer control unit 1. It is composed of a comparator 252 that outputs a comparison result with a counter value by the main scanning counter 251 and a gate signal generation unit 253 that generates a main scanning gate signal XRGATE based on the comparison result from the comparator 252.

The sub-scanning control signal generation unit 260 includes an image formation start signal from the printer control unit 1, a sub-scanning counter 261 that operates with the signal XLSYNC and the pixel clock signal PCLK, a counter value, and correction data after passing through the printer control unit 1. It is composed of a comparator 262 that compares the second set value SET2 included in the above and outputs the result, and a gate signal generation unit 263 that generates a sub-scanning gate signal XFGATE from the comparison result from the comparator.

The writing start position control unit 222 corrects the writing position in units of one cycle of the pixel clock signal PCLK, that is, in units of one dot in the main scanning direction, and in units of one cycle of the signal XLSYNC in the sub-scanning direction, that is, in units of one line. The writing position can be corrected with.

<Operation of writing position control by the image forming apparatus 100>
Next, the operation of the writing start position control by the image forming apparatus 100 will be described with reference to FIG. In the following description, the synchronization detection signal XDETP, the counter operation signal XLSYNC, the main scanning gate signal XRGATE, and the sub-scanning gate signal XFGATE will be described as an example in which a low level is valid signal, that is, a low active signal.

FIG. 9 is a timing chart illustrating an example of writing start position control in the main scanning direction by the image forming apparatus 100.

The main scan counter is reset by the counter operation signal XLSYNC. The main scanning counter is a count value obtained by the main scanning counter 251 in FIG. The main scanning counter 251 counts up according to the pixel clock signal PCLK. When the count value of the main scanning counter 251 becomes the first set value SET1, the comparator 252 for main scanning outputs a signal of the comparison result. In the example of FIG. 9, the first set value SET1 is displayed as "X".

Next, when a signal indicating that the first set value SET1 is reached is output from the comparator 252 for main scanning, the main scanning control signal generation unit 250 lowers the main scanning gate signal XRGATE. The main scanning gate signal XRGATE is a signal that becomes low level only during a period corresponding to the width of the toner image in the main scanning direction.

FIG. 10 is a timing chart illustrating an example of writing start position control in the sub-scanning direction by the image forming apparatus 100.

The print start signal SRT resets the sub-scan counter. The sub-scanning counter is a count value by the sub-scanning counter 261 shown in FIG.

The sub-scanning counter 261 counts up by the counter operation signal XLSYNC. When the count value by the sub-scanning counter 261 becomes the second set value SET2, the comparator 262 for sub-scanning outputs the signal of the comparison result. In the example of FIG. 10, the second set value SET2 is displayed as "Y".

Next, when a signal indicating that the second set value is SET2 is output from the comparator 262 for sub-scanning, the sub-scanning control signal generation unit 260 lowers the sub-scanning gate signal XFGATE. The sub-scanning gate signal XFGATE is a signal that becomes low level only for a period corresponding to the width of the toner image in the sub-scanning direction.

<Configuration of line memory LMEM>
Next, FIG. 11 is a diagram illustrating an example of the configuration of the line memory LMEM included in the image forming apparatus 100. The line memory LMEM is provided in the front stage of the hardware configuration around the light beam scanning unit 21 shown in FIG.

The line memory LMEM stores image data captured from the printer controller, frame memory, scanner, or the like at the timing indicated by the sub-scanning gate signal XFGATE or the like. Further, it is assumed that the stored image data is synchronized with the pixel clock signal PCLK and a signal for several beams is output. Further, the signal output from the line memory LMEM is output to the LD control unit 223, and the LD211 is controlled so as to light up at the timing indicated by the signal.

<Example of image forming operation by the image forming apparatus 100>
Next, the image forming operation by the image forming apparatus 100 will be described with reference to FIG. FIG. 12 is a flowchart showing an example of an image forming operation by the image forming apparatus 100.

First, in step S121, when the start button on the operation panel of the image forming apparatus 100 is pressed, the polygon motor control unit 221 rotates the polygon motor in response to an instruction from the printer control unit 1 to rotate the polygon mirror 213. Rotate at a predetermined number of rotations.

Subsequently, in step S122, the printer control unit 1 reads out the correction data for correcting the writing start position of the main scan and the sub scan, the main scan magnification, and the like from the correction data storage unit 229. Then, the output is output to the polygon motor control unit 221, the writing start position control unit 222, the LD control unit 223, the synchronization detection lighting control unit 224, and the pixel clock generation unit 225. Each control unit sets the input correction data.

Subsequently, in step S123, the synchronization detection lighting control unit 224 lights the LD211 and performs an APC (Automatic Power Control) operation or the like in order to light the LD with a predetermined amount of light.

Subsequently, in step S124, the polygon motor control unit 221, the writing start position control unit 222, the LD control unit 223, the synchronization detection lighting control unit 224, and the pixel clock generation unit 225 work together to form an image.

Subsequently, in step S125, the printer control unit 1 determines whether or not there is an image to be formed next.

If it is determined in step S125 that there is an image to be image-formed next (step S125, Yes), the process returns to step S124, and image formation is performed again. On the other hand, if it is determined in step S125 that there is no image to be formed next (step S125, No), the process proceeds to step S126, and the LD control unit 223 responds to an instruction from the printer control unit 1 to perform LD211. Turns off.

Subsequently, in step S127, the polygon motor control unit 221 stops the rotation of the polygon motor in response to the instruction from the printer control unit 1, and the image forming operation ends.

In this way, the image forming apparatus 100 can form an image on the recording medium P.

[First Embodiment]
<Example of functional configuration of printer control unit 1>
Next, the functional configuration of the printer control unit 1 will be described with reference to FIG. FIG. 13 is a block diagram illustrating an example of the functional configuration of the printer control unit 1.

As shown in FIG. 13, the printer control unit 1 includes a print mode detection unit 11 and a color shift correction unit 12.

Of these, the print mode detection unit 11 detects the print mode by the image forming apparatus 100 and outputs the detection result to the color shift correction unit 12. The print mode detection unit 11 can detect the print mode by referring to the print condition information input via the operation panel for operating the image forming apparatus 100, the host PC for instructing printing, and the like.

The color shift correction unit 12 corrects color shift in an image formed of a plurality of colors. Further, in the case of the first printing mode in which the image is formed by using the reference color, the color shift correction unit 12 is a correction toner image formed of a color other than the reference color with respect to the correction toner image formed of the reference color. Corrects color misalignment based on misalignment. Further, in the case of the second print mode in which the image is formed without using the reference color, the color shift is corrected based on the positional shift between the correction toner images formed for each of a plurality of colors used in the image formation.

In this color shift correction, the color shift correction unit 12 determines the amount of misalignment of each color and the position shift amount of each color based on the voltage signals detected by the first sensor 31 and the second sensor 32 for the correction toner image formed on the intermediate transfer belt 10. The magnification error in the main scanning direction and its correction data are acquired. The acquired correction data is output to each of the writing start position control unit 222, the pixel clock generation unit 225, and the correction data storage unit 229, and the correction data is set.

The writing start position control unit 222 in the optical beam scanning unit 21 controls the writing start positions in the main scanning direction and the sub-scanning direction according to the correction data acquired with reference to the correction data storage unit 229. As a result, the positional deviation in the main scanning direction and the sub scanning direction for each color is corrected. Further, the pixel clock generation unit 225 generates a pixel clock according to the correction data to correct the magnification error in the main scanning direction.

<Example of color shift correction processing in the first print mode>
Here, the correction process by the color shift correction unit 12 in the first print mode will be described in detail with reference to FIG. In the first print mode, the color shift is corrected based on the positional shift of the correction toner image formed of a color other than the reference color with respect to the correction toner image formed of the reference color.

Here, FIG. 14 is a diagram illustrating an example of a correction toner image detected by the first sensor 31 and the second sensor 32, and is a diagram for correcting correction formed on the intermediate transfer belt 10 traveling in the traveling direction 5. It shows a toner image. Note that FIG. 14 is a correction toner image corresponding to the configuration of the image forming unit 20 shown in FIG.

W1 to W4 represent a white (W) correction toner image, M1 to M4 represent a magenta (M) correction toner image, and K1 to K4 represent a black (K) correction toner image. Further, Y1 to Y4 represent a yellow (Y) correction toner image, and C1 to C4 represent a cyan (C) correction toner image.

The first sensor 31 arranged on the upstream side of the main scanning direction 102 (left side in FIG. 14) has the correction toner images W1, M1, K1, Y1, C1, W3, formed on the upstream side of the main scanning direction 102. Detects M3, K3, Y3 and C3. The first sensor 31 detects these correction toner images that move as the intermediate transfer belt 10 travels, and outputs a voltage signal whose voltage changes in time series to the color shift correction unit 12.

The second sensor 32 arranged on the downstream side of the main scanning direction 102 (on the right side of FIG. 14) has the correction toner images W2, M2, K2, Y2, C2, W4, formed on the downstream side of the main scanning direction 102. Detects M4, K4, Y4 and C4. Similarly, the second sensor 32 detects these correction toner images that move as the intermediate transfer belt 10 travels, and outputs a voltage signal whose voltage changes in time series to the color shift correction unit 12.

The correction toner images W1 to W4, M1 to M4, K1 to K4, Y1 to Y4, and C1 to C4 constitute the correction toner image group 140.

The color shift correction unit 12 can acquire the position of each correction toner image from the timing when the voltage signal input from the first sensor 31 and the second sensor 32 becomes a voltage value corresponding to the correction toner image.

In the first printing mode, the correction is performed using black (K) formed by the most downstream image forming portion in the traveling direction 5 of the intermediate transfer belt 10 as a reference color. Therefore, the positions of the toner images of each color with respect to the positions of the black (K) correction toner images K1 to K4 are acquired.

Of the correction toner image group 140, the correction toner images W3 to W4, M3 to M4, K3 to K4, Y3 to Y4, and C3 to C4 of the diagonal lines are for acquiring the positional deviation and the magnification error in the main scanning direction. Used for. Further, in the correction toner image group 140, the horizontal line correction toner images W1 to W2, M1 to M2, K1 to K2, Y1 to Y2, and C1 to C2 are used to acquire the amount of misalignment in the sub-scanning direction. Used.

A more specific description will be given by taking the correction toner images C1 to C4 of cyan (C) as an example. First, color shift correction in the main scanning direction will be described.

The color shift correction unit 12 has an elapsed time tk1 from the detection of the correction toner image C1 to the detection of the correction toner image C3 with respect to the elapsed time tk1 from the detection of the correction toner image K1 to the detection of the correction toner image K3. Acquire the time difference TKC13. Further, the time difference TKC24 of the elapsed time tk2 from the detection of the correction toner image C2 to the detection of the correction toner image C4 with respect to the elapsed time tk2 from the detection of the correction toner image K2 to the detection of the correction toner image K4 is acquired.

The time difference value between the time difference TKC24 and the time difference TKC13 becomes a magnification error in the main scanning direction of the cyan (C) toner image with respect to the black (K) toner image. The magnification error in the main scanning direction is stored in the correction data storage unit 229 as correction data. The pixel clock generation unit 225 corrects the magnification error in the main scanning direction by changing the frequency of the pixel clock according to the magnification error in the main scanning direction.

Further, the value obtained by subtracting the above time difference value at the position of the first sensor 31 from the time difference TKC 13 is the amount of misalignment of the cyan (C) toner image with respect to the black (K) toner image in the main scanning direction. The amount of misalignment in the main scanning direction is stored in the correction data storage unit 229 as correction data. The writing start position control unit 222 corrects the misalignment amount in the main scanning direction by changing the timing of the main scanning gate signal XRGATE for determining the writing start timing according to the misalignment amount in the main scanning direction. ..

In this way, the color shift in the main scanning direction with respect to the cyan (C) toner image is corrected.

Next, color shift correction in the sub-scanning direction will be described. Here, the ideal time is Tc, and the elapsed time from the detection of the correction toner image K1 to the detection of the correction toner image C1 is TKC1. Further, the elapsed time from the detection of the correction toner image K2 to the detection of the correction toner image C2 is defined as TKC2.

By calculating ((TKC2 + TKC1) / 2) -Tc using these, the amount of misalignment of the cyan (C) toner image with respect to the black (K) toner image in the sub-scanning direction can be obtained. The amount of misalignment in the sub-scanning direction is stored in the correction data storage unit 229 as correction data. The writing start position control unit 222 corrects the misalignment amount in the sub-scanning direction by changing the timing of the sub-scanning gate signal XFGATE for determining the writing start timing according to the misalignment amount in the sub-scanning direction. ..

In this way, the color shift in the sub-scanning direction with respect to the cyan (C) toner image is corrected.

Further, by using the correction toner image of cyan (C) as an example and performing the above-mentioned correction processing using the correction toner images of other colors yellow (Y), magenta (M), and white (W), It is possible to correct the color shift in the main scanning direction and the sub scanning direction of each color and the magnification error in the main scanning direction.

In the embodiment, the correction toner image of the diagonal line and the horizontal line pattern is illustrated, but the pattern is not limited to this, and any pattern can be used. Further, although an example in which the correction toner image is formed at two places in the main scanning direction is shown, the present invention is not limited to this, and the correction toner image may be formed at three or more places.

Further, in the embodiment, an example of correcting the color shift using one set of correction toner image groups is shown, but a plurality of sets of correction toner image groups 140 formed on the intermediate transfer belt 10 along the traveling direction 5 It is also possible to correct the color shift using. In this case, the average of the displacement amount in the main scanning direction, the magnification error in the main scanning direction, and the displacement amount in the sub-scanning direction obtained by using each of the plurality of sets of correction toner image groups 140. The value is used as correction data. As a result, it is possible to acquire correction data in which the detection error is reduced by the averaging effect.

Next, FIG. 15 is a diagram showing an example of a correction toner image corresponding to the configuration of the image forming unit 20 shown in FIG. As shown in FIG. 15, the correction toner images K1 to K4, M1 to M4, W1 to W4, Y1 to Y4, and C1 to C4 have the colors of the correction toner image as compared with the correction toner image group 140. The order of arrangement is changed to form the correction toner image group 140a.

The reference color is white (W) by the image forming unit 20 arranged at the most downstream in the traveling direction 5. For each color other than white (W), the color shift is corrected based on white (W). Since the correction process is the same as that described with reference to FIG. 14, only the reference color is different, duplicate description will be omitted here.

<Example of color shift correction processing in the second print mode>
Next, the correction process by the color shift correction unit 12 in the second print mode will be described. In the second print mode, since the reference color is not used in the image formation, the color shift is corrected based on the positional shift between the correction toner images formed for each of the plurality of colors used in the image formation. More specifically, among the plurality of correction toner images for each color used in image formation, the center position between the two correction toner images having the largest misalignment is set as the reference position, and the correction toner image of each color with respect to this reference position is used. Correct the misalignment of.

Here, FIG. 16 is a diagram showing an example of a correction toner image corresponding to the configuration of the image forming unit 20 shown in FIG. As shown in FIG. 16, the correction toner images K1 to K4, M1 to M4, Y1 to Y4, and C1 to C4 constitute the correction toner image group 140b.

Here, as in FIG. 15, the reference color is white (W) by the image-forming unit 20 arranged at the most downstream in the traveling direction 5. However, as shown in FIG. 4, the most downstream image forming unit 20 does not form a toner image apart from the transfer unit 62 and the intermediate transfer belt 10. In other words, it is in the second print mode in which an image is formed without using white (W), which is a reference color. As shown in FIG. 16, the correction toner image group 140b formed on the intermediate transfer belt 10 in the second print mode does not include the white (W) correction toner images W1 to W4.

In the embodiment, first, the amount of misalignment between the correction toner images of each color used in image formation is acquired. As an example, in the main scanning direction, the amount of misalignment of the correction toner image of each color with respect to the correction toner image of black (K) as a temporary reference color is acquired, and the main scanning direction between the correction toner images of each color is obtained. Acquires the amount of misalignment and magnification error of.

Further, in the sub-scanning direction, the ideal time is Tc, and the elapsed time from the detection of the correction toner image K1 to the detection of the correction toner image C1 is TKC1. Further, the elapsed time from the detection of the correction toner image K2 to the detection of the correction toner image C2 is defined as TKC2.

By calculating ((TKC2 + TKC1) / 2) -Tc using these, the amount of misalignment of the cyan toner image with respect to the black toner image in the sub-scanning direction is obtained.

Similarly for other magenta (M) and yellow (Y), the amount of misalignment in the main scanning direction, the magnification error in the main scanning direction, and the sub-scanning direction are based on the amount of misalignment with respect to black (K) as the temporary reference color. Get the amount of misalignment of.

<Calculation of reference position>
Here, in the sub-scanning direction, the amount of misalignment of the cyan (C) correction toner image with respect to the black (K) correction toner image is KC, and the magenta (M) with respect to the black (K) correction toner image. Let KM be the amount of misalignment of the correction toner image. Further, the amount of misalignment of the yellow (Y) correction toner image with respect to the black (K) correction toner image is defined as KY.

FIG. 17 shows an example of the positional relationship between these misalignment amounts KC, KM, and KY. Here, FIG. 17 is a diagram illustrating an example of a reference position.

In the example of FIG. 17, the two correction toner images having the largest misalignment among the correction toner images of each color are the correction toner images of yellow (Y) and magenta (M). In the embodiment, a position corresponding to 1/2 of the amount of misalignment between the yellow (Y) correction toner image and the magenta (M) correction toner image is set as a reference position in the sub-scanning direction. The reference position 171 shown by the broken line in FIG. 17 corresponds to the reference position in the sub-scanning direction. Based on this reference position, the amount of misalignment of the toner image of each color is corrected.

Specifically, in the case of black (K), KM-YM / 2 is acquired as a misalignment amount (correction data) in the sub-scanning direction and stored in the correction data storage unit 229. The writing start position control unit 222 corrects the misalignment amount in the sub-scanning direction by changing the timing of the sub-scanning gate signal XFGATE for determining the writing start timing according to the misalignment amount in the sub-scanning direction.

<Example of color shift correction operation by the image forming apparatus 100>
Next, the color shift correction operation by the image forming apparatus 100 will be described with reference to FIG. FIG. 18 is a flowchart showing an example of a color shift correction operation by the image forming apparatus 100.

Here, the printer control unit 1 controls the execution timing of the color shift correction in the image forming apparatus 100. The printer control unit 1 executes color shift correction for each predetermined number of prints, or when the temperature is monitored and the temperature changes more than a predetermined value.

First, in step S181, the print mode detection unit 11 detects the print mode by the image forming apparatus 100 and outputs the detection result to the color shift correction unit 12.

Subsequently, in step S182, the optical beam scanning unit 21 sets the main scanning gate signal XRGATE, the sub-scanning gate signal XFGATE, and the pixel clock frequency according to the correction data acquired with reference to the correction data storage unit 229.

Subsequently, in step S183, the light beam scanning unit 21 cooperates with the image forming unit 20 to form the correction toner image group 140 on the intermediate transfer belt 10.

Subsequently, in step S184, the first sensor 31 and the second sensor 32 detect the correction toner image of each color included in the correction toner image group 140.

Subsequently, in step S185, the color shift correction unit 12 determines whether or not the print mode is the first print mode.

If it is determined in step S185 that the print mode is the first print mode (steps S185, Yes), in step S186, the color shift correction unit 12 has a reference color with respect to the correction toner image formed of the reference color. The amount of misalignment in the main scanning direction and the sub-scanning direction of the correction toner image formed in a color other than the above and the magnification error in the main scanning direction are calculated and acquired.

On the other hand, when it is determined in step S185 that the print mode is not the first print mode (steps S185, No), in step S187, the color shift correction unit 12 is a toner image for correcting a plurality of colors used in image formation. The reference position is acquired by calculating the center position between the two correction toner images having the largest misalignment.

Subsequently, in step S188, the color shift correction unit 12 determines the amount of position shift of the correction toner images formed of the plurality of colors used in image formation in the main scanning direction and the sub scanning direction with respect to the reference position, and the main. The magnification error in the scanning direction is calculated and acquired.

The amount of misalignment of the correction toner images in the main scanning direction and the sub-scanning direction and the magnification error in the main scanning direction in steps S186 and S188 are such that a plurality of sets of correction toner image groups 140 are formed on the intermediate transfer belt 10. If this is the case, it is acquired as an average value based on the detection results of a plurality of sets of correction toner image groups 140.

Subsequently, in step S189, the color shift correction unit 12 determines whether or not to correct the color shift. In this determination, if the amount of misalignment is 1/2 or more of the correction resolution of misalignment, it is determined that color misalignment correction is performed, and if it is not 1/2 or more, it is determined that color misalignment correction is not performed.

If it is determined in step S189 that the color shift is to be corrected (step S189, No), the image forming apparatus 100 ends the operation.

On the other hand, when it is determined in step S189 that the color shift is corrected (step S189, Yes), in step S190, the color shift correction unit 12 receives the correction data of the position shift in the main scanning direction and the sub scanning direction and the correction data. Acquires correction data for magnification error in the main scanning direction. The correction data here are the set value of the main scanning gate signal XRGATE that determines the image position in the main scanning direction, the set value of the sub-scanning gate signal XFGATE that determines the image position in the sub-scanning direction, and the image magnification in the main scanning direction. It is a set value of the pixel clock frequency that determines. The color shift correction unit 12 outputs the acquisition result to the correction data storage unit 229.

Subsequently, in step S191, the correction data storage unit 229 stores the correction data for the misalignment and the magnification error.

Subsequently, in step S192, the optical beam scanning unit 21 sets the main scanning gate signal XRGATE, the sub-scanning gate signal XFGATE, and the pixel clock frequency according to the correction data acquired with reference to the correction data storage unit 229.

In this way, the image forming apparatus 100 can correct the color shift.

<Action and effect of the image forming apparatus 100>
As described above, in the embodiment, the color shift correction unit 12 for correcting the color shift of the image formed by a plurality of colors is provided, and the color shift correction unit 12 does not use a predetermined reference color for the image. In the case of the second print mode to be formed, the color shift is corrected based on the positional shift between the correction toner images formed for each of a plurality of colors used in the image formation.

As a result, even in the second print mode in which the image is formed without using the reference color, it is not necessary to switch to the first print mode in which the image is formed using all the colors including the reference color, and the color shift is maintained in the second print mode. Can be corrected. As a result, productivity can be ensured and color shift can be corrected.

Further, in the embodiment, the color shift correction unit 12 corrects the color shift based on the position shift between the two correction toner images having the largest misalignment among the correction toner images of each color. More specifically, the color shift correction unit 12 uses the center position between the two correction toner images having the largest misalignment among the correction toner images of each color as the reference position, and the misalignment of the correction toner image of each color with respect to the reference position. To correct. As a result, the maximum positional deviation can be corrected so as to be minimized, so that the fluctuation of the color deviation can be suppressed before and after the correction to correct the color deviation.

Further, in the embodiment, in the first print mode, the color shift correction unit 12 shifts the color based on the positional shift of the correction toner image formed of a color other than the reference color with respect to the correction toner image formed of the reference color. In the second print mode, the color shift is corrected based on the positional shift between the correction toner images formed of a plurality of colors used in image formation. As a result, in the first print mode, the color shift with respect to the reference color can be corrected, so that the color shift can be corrected with higher accuracy, and in the second print mode, the productivity can be secured and the color shift can be corrected.

[Second Embodiment]
Next, the image forming apparatus 100a according to the second embodiment will be described.

FIG. 19 is a block diagram showing an example of the functional configuration of the printer control unit 1a included in the image forming apparatus 100a. As shown in FIG. 19, the printer control unit 1a includes a color shift correction unit 12a.

In the first color shift correction after switching from the first print mode to the second print mode, the color shift correction unit 12a shifts the position between the correction toner images formed for each of a plurality of colors used in image formation. Make corrections based on. Further, in the second and subsequent color shift corrections, the position shift of the correction toner image formed of a color other than the predetermined color with respect to the correction toner image formed of the predetermined color among the plurality of colors used in the image formation is used. Make corrections. As a result, after switching from the first print mode to the second print mode, in the first color shift correction, productivity is ensured and the fluctuation of the color shift is suppressed before and after the correction to correct the color shift. In the color shift correction, the process is simplified and corrected.

Next, the color shift correction operation by the image forming apparatus 100a will be described with reference to FIG. FIG. 20 is a flowchart showing an example of a color shift correction operation by the image forming apparatus 100a. The operation of steps S201 to S206 in FIG. 20 is the same as that of steps S181 to S186 in FIG. The operation of steps S210 to S215 is the same as that of steps S187 to S192 in FIG. Therefore, these duplicate descriptions will be omitted here.

In step S207, the color shift correction unit 12a determines whether or not the correction is the first time after switching from the first print mode to the second print mode. This determination can be made by counting the number of times the correction is executed and referring to the count number stored in the RAM or the like of the printer control unit 1a.

If it is determined in step S207 that the correction is not the first correction (step S207, No), in step S208, the color shift correction unit 12a selects a predetermined color as a reference among the plurality of colors used in image formation. decide. For example, black (K) is set as a predetermined color.

Subsequently, in step S209, the color shift correction unit 12a determines the amount of misalignment in the main scanning direction and the sub-scanning direction of the correction toner image formed in a color other than the predetermined color with respect to the correction toner image formed in the predetermined color. And, the magnification error in the main scanning direction is calculated and acquired.

In this way, the image forming apparatus 100a can correct the color shift.

As described above, in the present embodiment, the color shift correction unit 12a performs the first color shift correction after switching from the first print mode to the second print mode for each of a plurality of colors used in image formation. Correction is performed based on the positional deviation between the formed correction toner images. Further, in the second and subsequent color shift corrections, correction is made based on the positional shift of the correction toner image formed of a color other than the predetermined color with respect to the correction toner image formed of the predetermined color among the plurality of colors used in the image formation. I do.

As a result, in the first color shift correction after switching from the first print mode to the second print mode, productivity can be ensured and fluctuations in color shift can be suppressed before and after the correction. Further, in the second and subsequent color shift corrections, the process of acquiring the reference position can be omitted, so that the process can be further simplified and corrected.

Although examples of embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and various aspects are described within the scope of the gist of the present invention described in the claims. It can be transformed and changed.

In the embodiment, an example of correcting the color shift by using the correction toner image formed on the intermediate transfer belt 10 is shown, but the present invention is not limited to this. In the case of a so-called direct transfer type image forming apparatus that transfers a toner image directly from the photoconductor drum 40 to the recording medium P without passing through the intermediate transfer belt 10, the toner image is formed on the transfer body to be transferred to the recording medium P. It is also possible to correct the color shift by using the correction toner image. Further, the color shift correction is not limited to the correction toner image formed on the image carrier, and the color shift correction may be performed using the correction toner image (correction printed image) formed on the recording medium P. Good.

Further, in the embodiment, the electrophotographic image forming apparatus has been described, but the present invention is not limited to this, and other image forming methods such as the inkjet method also cause color shift in image forming using a plurality of colors. The embodiment can be applied to the amendment.

The embodiment also includes a color shift correction method. For example, the color shift correction method is a color shift correction method using an image forming apparatus that forms an image with a plurality of colors, and when an image is formed without using a predetermined reference color, each of the plurality of colors used in the image formation is used. The correction is performed based on the positional deviation between the formed pattern images. By such a color shift correction method, the same effect as that of the image forming apparatus described above can be obtained.

Each function of the embodiment described above can be realized by one or more processing circuits. Here, the "processing circuit" in the present specification is a processor programmed to execute each function by software such as a processor implemented by an electronic circuit, or a processor designed to execute each function described above. It shall include devices such as ASIC (Application Specific Integrated Circuit), DSP (digital signal processor), FPGA (field programmable gate array) and conventional circuit modules.

1 Printer control unit 5 Traveling direction 10 Intermediate transfer belt (an example of image carrier)
11 Print mode detection unit 12 Color shift correction unit 21 Light beam scanning unit 31 First sensor 32 Second sensor 40 Photoreceptor drum 100 Image forming device 140 Correction toner image group 171 Reference position 210 Scanning optical system 221 Polygon motor control unit 222 Writing start position control unit 223 LD control unit 224 Synchronous detection lighting control unit 225 Pixel clock generation unit 229 Correction data storage unit P Recording medium W1 to W4 White (example of reference color) correction toner image M1 to M4 Magenta ( Correction toner image K1 to K4 of (an example of a color used in image formation) Correction toner image of black (an example of a color used in image formation) Y1 to Y4 Yellow (an example of a color used in image formation) correction toner image C1 ~ C4 Cyan (an example of colors used in image formation) correction toner image

Japanese Unexamined Patent Publication No. 2008-51943

Claims (8)

Equipped with a color shift correction unit that corrects color shifts in images formed by multiple colors.
The color shift correction unit is
When an image is formed without using a predetermined reference color, the image forming apparatus performs the correction based on the positional deviation between the pattern images formed for each of a plurality of colors used in the image forming. The image forming apparatus according to claim 1, wherein the color shift correction unit performs the correction based on the positional shift between the two pattern images having the largest misalignment among the pattern images of each color. The color shift correction unit uses the central position between the two pattern images having the largest misalignment among the pattern images of each color as a reference position, and corrects the pattern image based on the misalignment of the pattern image of each color with respect to the reference position. The image forming apparatus according to claim 1 or 2. The color shift correction unit is
In the case of the first printing mode in which an image is formed using the reference color, the correction is performed based on the positional deviation of the pattern image formed in a color other than the reference color with respect to the pattern image formed in the reference color. ,
In the case of the second print mode in which an image is formed without using the reference color, claims 1 to 3 in which the correction is performed based on the positional deviation between the pattern images formed for each of a plurality of colors used in the image formation. The image forming apparatus according to any one item. The color shift correction unit is
In the first correction after switching from the first print mode to the second print mode, the correction is performed based on the positional deviation between the pattern images formed for each of a plurality of colors used in the image formation. The image forming apparatus according to claim 4. The color shift correction unit is
In the second and subsequent corrections after switching from the first print mode to the second print mode, other than the predetermined color with respect to the pattern image formed by the predetermined color among the plurality of colors used in the image formation. The image forming apparatus according to claim 5, wherein the correction is performed based on the positional deviation of the pattern image formed in the above colors. The image forming apparatus according to any one of claims 1 to 6, wherein the pattern image is a toner image formed on an image carrier. This is a color shift correction method using an image forming apparatus that forms an image with a plurality of colors.
When an image is formed without using a predetermined reference color, the color shift correction method performs the correction based on the positional shift between the pattern images formed for each of a plurality of colors used in the image formation.

Images